In one known form of dual spindle NC chucking/turning machine dual turrets with tool holders thereon are fixedly mounted on a tool slide for automatically performing identical machining operations on workpieces chucked on the respective spindles in response to NC control of the movements and positions of the main slide and tool slide on perpendicularly related axes parallel to the spindle axes (Z-axis) and transverse to the spindle axes (X-axis). However, in the event of uneven tool wear, temperature differences, and tool presetting errors the machined surfaces of the workpieces will vary and cannot be compensated for by the tool offset controls of the tool slide on the X-axis.
The foregoing problem of compensating for uneven tool wear, temperature differences, and tool presetting errors has been solved by providing a main tool slide on which a first turret is fixed and providing an auxiliary tool slide on the main tool slide for a second turret so that the latter may be adjusted by shifting the auxiliary tool slide independently of the main tool slide. When adjustment of the tool offset of the first turret is necessary, a summing circuit is provided which will cause the auxiliary tool slide on which the second turret is mounted to compensate for the main tool slide movement. Reference may be had to the U.S. Pat. No. 3,754,178 to Dormehl et al granted Aug. 21, 1973 for an apparatus including such summing circuit to compensate for tool wear in a multi-spindle machine tool in which a first tool is fixed on a motor-driven cross-slide and a second tool on an auxiliary tool slide is adjustable on the cross-slide by an auxiliary tool slide drive so that in the event of tool offset adjustment of the tool on the cross-slide, the summing circuitry operates the tool adjusting mechanism for the second tool to maintain a constant spacing between the working edges of the first and second tools.